The presence of large amounts of nondiamond carbon in detonation-synthesized nanodiamond (ND) severely limits applications of this exciting nanomaterial. We report on a simple and environmentally friendly route involving oxidation in air to selectively remove sp(2)-bonded carbon from ND. Thermogravimetric analysis and in situ Raman spectroscopy shows that sp(2) and sp(3) carbon species oxidize with different rates at 375-450 degrees C and reveals a narrow temperature range of 400-430 degrees C in which the oxidation of sp(2)-bonded carbon occurs with no or minimal loss of diamond. X-ray absorption near-edge structure spectroscopy detects an increase of up to 2 orders of magnitude in the sp(3)/sp(2) ratio after oxidation. The content of up to 96% of sp(3)-bonded carbon in the oxidized samples is comparable to that found in microcrystalline diamond and is unprecedented for ND powders. Transmission electron microscopy and Fourier transform infrared spectroscopy studies show high purity 5-nm ND particles covered by oxygen-containing surface functional groups. The surface functionalization can be controlled by subsequent treatments (e.g., hydrogenization). In contrast to current purification techniques, the air oxidation process does not require the use of toxic or aggressive chemicals, catalysts, or inhibitors and opens avenues for numerous new applications of nanodiamond.
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"Both processes lead to the formation of carbon–hydrogen bonds on the DND surface and the formation of positive zeta potential in colloidal solution of hydrogenated H-DNDs  . Oxygen termination of DNDs is typically achieved by annealing in air at temperatures between 400–500 °C  . In contrast to H-DNDs the formation of functional groups containing oxygen on the surface of DNDs leads to a negative zeta potential of oxidized O-DNDs in colloidal solution  . "
"We attribute this result to the presence of residual O 2 in the furnace during the ramp-up stage. It has been shown that sp 2 and sp 3 carbon components of polycrystalline diamond can oxidize in presence of oxygen above 400 °C . The Q-factor for each cantilever was extracted from 10 consecutive ring-down time-responses measured using a lock-in amplifier (HF2LI, Zurich Instruments) and the average Q was recorded. "
[Show abstract][Hide abstract] ABSTRACT: This paper reports an investigation into the various dissipation mechanisms that can affect polycrystalline diamond micromechanical resonators. Double-ended tuning fork and cantilever resonators were fabricated from 1-5-μm thick microcrystalline diamond films. It is shown that the quality factor of the low frequency (<500 kHz) resonators is limited by surface loss, whereas the thermoelastic damping limits the quality factor of the higher frequency resonators. In resonators where surface loss is the dominant effect, the dependence of quality factor on resonator thickness is demonstrated. The addition of a lossy surface layer of Al₂O₃ deposited via atomic layer deposition is shown to degrade quality factor, and an experiment that further demonstrates the effect of surface dissipation and results in a reduction in quality factor that scales with the thickness of the Al₂O₃ layer. Heat treatment of cantilever resonators in N₂ for various times up to 660 min is used to modify the resonator surface and is shown to result in a threefold increase in quality factor up to 365,000 at 26.6 kHz. [2015-0094]
Full-text · Article · Oct 2015 · Journal of Microelectromechanical Systems
"The colour of the Pristine DND powder is Black and size of the DND clusters is below 500 nm as per the supplier's specifications. Pristine DND powder was oxidized at 435 C for 5 h to remove the impurities  . These impurities include traces of metals and nondiamond (amorphous and graphitic) carbon content . "
[Show abstract][Hide abstract] ABSTRACT: The aim of this study is the potential use of nanodiamond to make the lightweight and strong nanocomposites. Here, effects of size and surface modification of detonation nanodiamond (DND) on mechanical performance of epoxy based nanocomposites is presented. Our characterizations reveal that the process of functionalization not only removes the non-diamond content and impurities by significantly reducing DND's size but also introduces oxygen containing functional groups on its surface. The average size of functionalized DND aggregations could be decreased from 300 to 100 nm in contrast to pristine DND, which greatly benefits its homogeneous dispersion in epoxy matrix. In addition, strong chemical bonding among functionalized DND and epoxy resin due to functional groups leads to the formation of efficient interface. These interfaces overlap at high concentrations making a network which in turn significantly enhances the tensile properties. The enhancement in Young's modulus can reach up to 2.5 times higher than that of neat epoxy whereas the enhancement in tensile strength is about 1.5 times in functionalized DND/epoxy nanocomposites.
No preview · Article · Sep 2015 · Composites Part B Engineering